Need help, What battery do i need?

Re: Need help, What battery do i need?

btw nathan, mah is milliampere hours and you don't want that unless your goal is to recharge aa nicad or nimh rechargable batteries. for the record, 1000mah equals 1ah. from feedback i've read on the hf solar kit indicates it may give about 1.25a or so and the battery would range between 9.6ah and 25ah if that's so.

Re: Need help, What battery do i need?

The main problem with those kits is that they greatly exaggerate what you can do with them. As long as you understand you will NOT be running half your house off of it, they can be fun to play and learn with. There is also a problem with the panels, they are quite optimistic with their ratings. A few people have actually had good success and gotten near the 45W rating, most get nowhere near it.

And finally, the "charge controller" they supply is very crude. It basically just connects the panels directly to the battery until the voltage reaches a preset point, then disconnects until the voltage falls to another preset point. I found mine went way too high - right close to 15V - for my AGM battery. Might have gotten away with it for a flooded lead-acid battery, but didn't want to damage my (expensive!) AGM. I wound up buying a replacement controller from NAWS, and it works just fine with the panels.

Oh, almost forgot - at least with mine, there's a reason HF has a note to disconnect things after dark. The panels had no blocking diodes, when the battery voltage fell the controller "switched on", and I watched (on the WattsUp meter) current flow *backward* into the panels! Could have run the battery down overnight had I left it all connected. A better charge controller (like the one I replaced the HF one with) prevents this, or at the very least add a blocking diode to the panels.

I started with an HF kit, knowing full well what it is and isn't, so wasn't disappointed. My panels only give me about 20W output, to give you an idea of the ratings...

I used a 100AH AGM battery with my panels. That's right up to the top end as far as what the panels could possibly hope to keep up with, but my goal was to have only very shallow discharges on the battery for longevity, as well as have some reserve (that I would have to make up for by other means) in an outage. I used a "WattsUp" meter to watch power in and power out, found I could replace roughly 9AH per day with my panels. So I just made sure I used that much or less. Which was tough - that's not much power! On occasion I topped up the battery with a power supply from my ham bench.

I still use the HF set, even now that I have a much larger array of nicer panels. It makes for a handy battery-charging set to keep my collection of smaller AGM batteries ready to go.

Re: Need help, What battery do i need?

Bill,

"Irritates ... us" is probably too strong of term..."

I agree it is a bad choice of words. When I suggest that it "irritates us" what I mean is that it is a source of irritation that there is still a plethora of shoddy stuff out there ,, and that through no fault of their own, folks like Nathan spend money that might otherwise go to good Pv stuff,, potentially leaving them with a bad taste in their mouths regarding Pv.

I didn't mean to suggest in any way that I (or anyone else) was irritated at Nathan (or anyone else). It is an irritation at HF, Ebay junk etc. I hope that clarifies my point,, no offense intended.

Tony

Re: Need help, What battery do i need?

Sorry for your disappointment.

The reality is, as has been suggested often before,, one has to do the math. That is you have to start with your loads and work backwards to find the battery/Pv system that fits the load. So for example it doesn't mean much to ask,,"What kind of battery do I need to use with this panel?"

A proper question might be, "I have 45 watts of panel,, what can I run for how long with what battery?" Or, "I would like to run my lap top for 4 hours a day, what kind of panel and battery would you recommend?"

In the real world,, by my rule of thumb,, with a battery based system, you can count on About 1/2 the name plate rating of a good Pv panel, multiplied by the number of hours of good sun. Normal good sun rarely exceeds 4 hours per day.

So for example,, 100 watts of panel might be thus: 100/2*4(hours)=200 watt hours/day. So in this example, you could run a 50 watt lap top for ~4 hours.

All loads have to be expressed in both watts and time. One without the other means little. I suggest that for ~$20 you buy (or borrow) a Kill-a-watt meter. This simple meter will allow you to plug in your stuff, and it will tell you how many Kwhs it uses.

After you total all your loads,, you then can figure out how to power them. That said,, battery based Pv systems will run about double the cost of a Grid tied system.

Good luck, keep in touch

Tony

Re: Need help, What battery do i need?

NathanS have you seen the "u-tube" vids on those panels, Some people actually get some use out of them. And a couple shows their battery bank in the vid as well. Just type in solar panel in the search bar of u-tube.:cool:

Re: Need help, What battery do i need?

NathanS wrote: »

SO i just need a deep cycle 25amp/hour battery. If i tell a guy at a battery store that he will know what i need?

Depends on the guy and the store I guess.

Can i expect to have a battery hold a weeks worth of poer tou use later?

The more you want to store, the bigger the battery you'll need.

The 25 amp hour battery is the size for 150 watts per day of drain/recharge.

If you want to store a week's worth, then 25 amp hours x 7 = 175 amp hours.

But batteries self-drain as they sit, and they need a minimum amount of charging just to keep up with their self-draining. If the battery is too big, then that little HF kit won't put out enough juice to even keep it from self-draining.

And if you DON'T give it enough juice to keep up with the self-drain, then it won't last very long.